Various types of seals are used in rotating equipment, e.g., compressors, turbines, etc., to prevent or minimize gas leakage through mechanical clearances at both static and dynamic locations. In dynamic locations, such as around rotating shafts, shaft seals are typically positioned between a stationary housing and the rotating shaft. Shaft seals generally define a clearance between the outer surface of the shaft and the seal itself that allows the shaft to freely rotate, but which also inherently creates a leakage path for gas across the seal as a result of the seal clearance. In a compressor, for example, the shaft seal typically separates a high-pressure region from a low-pressure region and is designed to minimize the loss of high pressure working fluid through the clearance while also not interfering with the rotation of the shaft.
Labyrinth seals are often used to minimize fluid flow across a seal differential pressure. Labyrinth seals, however, generate higher “kxy” forces (i.e., forces in the “x” direction caused by shaft displacement in the “y” direction) which cause aero excitation and can create rotor instability. Another type of seal often used in rotating equipment is a damper seal, such as a see-through hole pattern or a honeycomb seal. Although damper seals advantageously exert higher damping forces on the shaft to attenuate shaft vibration, they often require a larger clearance than the typical labyrinth seal, and therefore, are not as effective at preventing axial leakage. Also, conventional damper seals do not allow for geometry modifications of the seal structure to optimize leakage and damping effect. Furthermore, damper seals, especially of the hole-pattern type, can often become plugged, thereby increasing gas leakage.
What is needed, therefore, is a seal that overcomes the disadvantages of prior seals by efficiently restricting gas leakage, while also providing stiffness and damping to the rotating machinery.